Electrical stimulation is a fundamental therapeutic modality that is indicated for pain management (TENS), drug delivery (Ionophoresis), and for treatment of a variety of neuromuscular conditions. Various terms are used to refer to electrical stimulation depending on the application and stimulus waveform used. Electrical stimulation with intensities sufficient to cause tetaneous contractions of skeletal muscle may result in muscle strengthening and/or joint/limb movement, and is termed Neuromuscular Electrical Stimulation (NMES) or Functional Electrical Stimulation (FES).
Electrical stimulation systems generate sequences of current pulses which excite motor neurons and in turn activate muscles. By changing the width, amplitude, or the frequency of the pulse train, the level of contraction can be altered to perform a specific task. In fitting an NMES system to an individual, a large set of parameters must be modified to account for each person's specific injury, anatomy, and muscle condition. The procedure for specifying these parameters requires a time-consuming trial-and-error process to find an appropriate set of parameters for each muscle. Since the same pulse train will be delivered for each contraction, the set of parameters that is suitable at the beginning of a session may not be appropriate after muscles fatigue. Similarly, day-to-day variability, nonlinearities of the musculoskeletal system, muscle response time, muscle conditioning, and joint constraints may hinder the effectiveness of even the best stimulation patterns.
Recovery of quadriceps muscle force following post-surgical knee immobilization is a significant therapeutic aim which is associated with quality of gait and the ability to perform activities of daily living. Several studies from various research groups have shown that neuromuscular electrical stimulation (NMES), used in conjunction with a comprehensive post-surgical rehabilitation program, is a safe and highly effective method for achieving quadriceps strengthening. Electrical stimulation has been widely studied as a technique indicated for quadriceps muscle strengthening for anterior cruciate ligament reconstruction (ACLR), total knee arthroplasty (TKA), and osteoarthritis. Efficacy of NMES for this application has been somewhat controversial, particularly in relation to the exercise protocol. Muscle strengthening outcomes of electrically stimulated exercise result not from the electrical stimulation itself but from the resulting muscle contraction; thus, stimulation protocols that do not elicit strong muscle contractions will have limited ability to build muscle.
Accordingly, it is desirable to develop a low cost, practical, cohesive system for quadriceps strengthening involving an NMES unit with autonomous, adaptive stimulation control capabilities in an outcome-based paradigm that does not require continuous involvement of the therapist. Another objective is to develop such a system that autonomously accounts for muscle fatigue during the exercise. A further goal is to develop an instrumented knee brace for use in such a system, capable of stabilizing the knee during near maximal isometric contractions and obtaining measurements of the resulting torque.